单项选择题
Rudder motion is prevented from exceeding the movement of the steering wheel by the（）
A.return springs B.six-way valve C.follow-up gear D.differential gear
单项选择题 Air trapped in the hydraulic fluid of a steering system may be indicated by（）
单项选择题 The purging of air from an elector-hydraulic steering gear unit is necessary when（）
单项选择题 If a severe leak develops in the electro-hydraulic steering gear unit is necessary when（）
